Hi, i am 17 years old and i realize that i should not be too concerned with irregular periods. However i have developed in all the other areas, like breasts and pubic hair. I get my period sometimes for 2 weeks or for a day, i can go without for several months. My lower abdomine gets very sore. I have gotten my blood tested and ultra sounds, but nothing was found. No other woman in my family have experienced this before. Should i be concerned or am i wasting my time?

The first year or so from the onset of your periods (menarche) it is not at all unusual to have such variability. You can just finish a period, go camping thinking you're "safe" then wham-o, here it comes again. So be prepared with protection at all times. Eventually it will probably level out to at least a somewhat predictable pattern, though being caught off guard is the nature of the game it seems.

The fact that all other development is on schedule makes me reassured you are doing fine.